1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, and a multi-function printer having a plurality of functions of those apparatuses and using an electro-photographic or electrostatic recording system.
2. Description of the Related Art
A two-component developer whose main components are toner and carrier is widely used for a developing apparatus provided in an electro-photographic or electro-static recording image forming apparatus. Because the toner within the developer is consumed during developments, toner concentration, i.e., a ratio of weight of the toner with respect to total weight of the carrier and the toner, varies as images are formed. Due to that, there is known a system controlling the toner concentration to an adequate range by replenishing the developer corresponding to changes of the toner concentration since the past as disclosed in Japanese Patent Application Laid-open No. H05-61353 for example.
There is also a possibility that the toner concentration within the developing apparatus drops sharply if images whose image ratio is high are consecutively formed. Then, hitherto, there is a control system interrupting an image forming operation and adjusting the toner concentration within the developing apparatus by forming a control patch when it is determined that a large amount of the toner is consumed based on information related to the toner consumption (toner replenishing amount) during a consecutive image forming job.
Even if the toner concentration can be adjusted by replenishing the developer as described above in the two-component developer system, the following problem may occur if the developer replenishing amount per unit sheet is excessive. That is, lately, the toner used in the two-component developer is endowed with low-temperature fixability from an aspect of energy saving. Such toner tends to coagulate and to form agglomerates when temperature rises. For instance, if a toner container storing such toner is left in a high-temperature and high-humidity place for a long period of time, there is a possibility that a large number of agglomerates is generated within the toner container.
If the developer is replenished from the toner container including the large number of such agglomerates into the developing apparatus, there is a case when the agglomerates contained in the replenished developer are held on a developing sleeve without being crushed in an agitating path within the developing apparatus. In such a case, there is a possibility that non-charged toner is developed where the agglomerates are held and an image is stained. Such stains tend to be remarkable in the case when the toner replenishing amount is excessive per unit sheet like a case when a plurality of images is formed consecutively with high image ratio. It is considered to happen because the agglomerates are not fully crushed due to lack of time of fully agitating and dispersing the developer within the developing apparatus because the toner is replenished continuously.
Still further, the agglomerates may not be fully crushed because the conventional control mode executed in a case when the toner consumption (replenishing amount) is large is carried out to adjust concentration and not to crush the agglomerates.